Acrylonitrile polymer spinning



Patented Oct. 9, 1951 AcaYLoNrrRmE POLYMER sPrNNrNG Herman A. Bruson, Shaker Heights, and Gilman S. Hooper, Bay Village, Ohio, assignors to Industrial Rayon Corporation, Cleveland, Ohio, a corporation of Delaware No Drawing. Application April 1, 1950, Serial No. 153,482

Claims. 1

This invention relates to a process for producing shaped articles such as fibers, ribbons, films, etc., by wet-spinning ethylene carbonate spinning solutions of acrylonitrile polymers and copolymers. More particularly, this invention is concerned with a spinning method which is capable of being conducted continuously for prolonged periods of time with improved efiiciency and yet without sacrificing uniformity, color or other desirable physical properties of the spun articles, hereinafter referred to as fibers. Further, it is concerned with a wet-spinning method in which the loss by decomposition, resinfication, etc. of the ethylene carbonate solvent and the coagulant employed is substantially minimized.

In the wet-spinning of ethylene carbonate spinning solutions of acrylonitrile polymers, spin bath compounds which are capable of coagulating such polymeric solutions usually present one or more of the following difliculties: ((1) the coagulant is poor in that weak fibers are produced or in that it can be used only at slow spinning speeds; (b) the coagulant causes excessive decomposition of the ethylene carbonate solvent, particularly when operating at elevated bath temperatures; (0) the coagulant, during spinning and bath recovery operations, decomposes and may form corrosive acidic materials or toxic decomposition products; such decomposition products may discolor the fibers.

The unstable nature of the ethylene carbonate solvent presents one of the difficulties which must be overcome to achieve successful wet-spinning of polymeric acrylonitrile solutions thereof. Since it is an ester, it undergoes hydrolysis in aqueous solutions, and particularly, under aqueous alkaline or acidic conditions. Moreover, this ester undergoes considerable transesterification in the presence of most alcohols, e. g. monohydric or polyhydric alcohols. The extent of such decomposition by hydrolysis or alcoholysis, is materially increased at the elevated temperatures which are employed during a spinning cycle such as, for example, elevated bath temperatures, e. g., 80 to 150 C., or elevated vacuum distillation temperatures for separating or purifying the bath components, or under both conditions.

Thus, for example, if a 20% solution of polyacrylonitrile (mol. wt. 50,000) in ethylene carbonate is extruded through a spinneret into a bath through which is circulating a mixture consisting of glycerol (85%) and ethylene carbonate maintained at 120-130 C. for a period of 100 hours, there is a prohibitive loss of such components in the bath. The extent of loss of such solvent and coagulant due only to resin formation (poly-glyceryl carbonate) by transesterification and formation of ethylene glycol, is found to be over 30% of the total weight of solvent and coagulant. If this spent spin bath is now distilled in vacuum at 5-10 m. m. for the purpose of recovering the ethylene carbonate and glycerol, it is found that very little ethylene carbonate distils over. Instead, an almost complete alcoholysis and breakdown takes place leading to the formation of lower boiling products among which glycidol is present. These reactions, in their simplest form, can be formulated as follows:

Similarly, the use of triethanolamine as a coagulant leads to a complete and immediate destruction of the ethylene carbonate as does the use of aqueous baths containing zinc halides or other inorganic salts.

Further, it has been found that the lower glycols notably ethylene glycol and its higher homologues such as propylene glycol, trimethylene glycol and 2,3,- or 1,3-butylene glycol, although showing a lesser tendency to undergo transesterification than glycerol, are nevertheless poor coagulants. With such coagulants, it is not only necessary to employ very low spinning speeds, but in addition, the yarns produced have excessive voids and low tenacit1es.

It has also been found that the higher glycols, some of which are capable of yielding good fibers at satisfactory speeds, undergo similar transesterification with ethylene carbonate when brought together as a heated coagulating bath liquid. ,Among these higher glycol coagulants may be mentioned the glycol ethers such as diethylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol, and other higher polyalkylene ether glycols. Among other types of higher glycols which readily transesterify ethylene carbonate may be mentioned 1,4-butanediol, 1,5-pentanediol, 2-methylpentanediol-2,4,thiodiglycol and other similar glycols. When such higher glycol coagulants are used as heated spinning baths and the used bath later distilled for the recovery of ethylene carbonate solvent and the coagulant, amounts up to from to 30%, depending upon the Particular glycol employed, may be lost due to transesterification and the formation of resinous polyester carbonates.

By the process of the present invention, the above difllculties encountered in the wet-spinning of ethylene carbonate solutions of acrylonitrile polymers are substantially eliminated, and fibers having desirable properties and appearance are produced with facility and efficiency. In this process, a new coagulant is employed which is relatively non-reactive with ethylene carbonate, thus, substantially minimizing solvent and coagulant losses due to decomposition, resinification, etc. In addition, the new coagulant can be easily washed from a freshly coagulated fiber by means of water, is non-corrosive, and further, is not only relatively free from toxicity but also possesses a low volatility which minimizes mechanical losses by evaporation, etc.

In accordance with the present invention, this accomplished by extruding an ethylene carbonate spinning solution of an acrylonitrile polymer containing a major portion of acrylonitrile into a liquid coagulating medium comprising dipropylene glycol.

In the discovery of the new coagulant of this invention, it was indeed surprising to find that dipropylene glycol should be different from all of the above-mentioned glycols in that when used as a coagulating bath for the wet-spinning of acrylonitrile polymer solutions in ethylene carbonate, it showed practically no transesterification with the ethylene carbonate and yet yielded high tenacity fibers at high spinning speeds.

For example, when a mixture consistingof 85% by weight of dipropylene glycol (substantially free from tripropylene glycol) and 15% by weight of ethylene carbonate was heated at 125-130 C. for 96 hours, thus simulating spinning conditions, less than 1% of transesterification occurred. Furthermore, when a mixture consisting of 350 parts by weight each of dipropylene glycol and ethylene carbonate was distilled in vacuum at m. m. pressure of meronly during the course of 6 hours, thus simulating bath-recovery and purification conditions, the still pot residue amounted to only 10 parts or 1.4% by weight of the total charge. I

The exact reason is not known for the unexpected difference in behavior of dipropylene glycol I as compared to its next lower homologue diethylene glycol HOCH2CH2OCH2CH2OH, and also to its next higher homologue tripropylene glycol,

CHICK-CHr-O-CHr-CH-O-CHz-CH-CHI H H; E

This behavior diflerence may be due, for example, to the differences in each compound in the relative positions of the two hydroxyl groups to each other, their secondary nature, other steric factors, or a combination of such factors.

In practicing the present invention, it is advantageous to employ a spin bath which, exclusive of the ethylene carbonate therein, consists for the most part, of dipropylene glycol.

The dipropylene glycol coagulant may, however, contain minor quantities of other materials or impurities such as,'for example, other polyhydric alcohol compounds. In general, as the quantities of such other material permitted in the new coagulant are diminished, the more beneficial and advantageous are the results. Thus, particularly advantageous results are derived when the spin bath, exclusive of ethylene carbonate, consists essentially of dipropylene glycol. If desired, technical and commercial grades of dipropylene glycol usually containing varying minor quantities of other polyhydric alcohol compounds may be conveniently employed. The presence of such extraneous polyhydric alcohol compounds in technical grade dipropylene glycol is usually due to the particular method of manufacture and refinement, if any. Among such extraneous materials may be mentioned ethylene glycol, diethylene glycol, propylene glycol, and tripropylene glycol. These may be found in the commercial products in quantities varying up to 5 or 10%, depending upon the source of the dipropylene glycol product and its method of manufacture. In general, these materials may be tolerated in amounts up to 20 to 25% by weight of the dipropylene glycol coagulant without undue adverse affect on the spinning process. In this connection, it is noteworthy that the amount of such extraneous materials in an operating coagulating bath will diminish after several cycles of recovery and purification of the coagulant by fractional distillation with the result that the coagulating bath will improve in eificiency with use.

The acrylonitrile polymer employed for the preparation of the spinning solutions may be polyacrylonitrile or copolymers of acrylonitrile containing in the polymer molecule a. major portion of acrylonitrile and with particular advantage over 80% acrylonitrile.

With repeated extrusion of the ethylene carbonate spinning solution into the spinning bath,

there is accumulated in the bath excessive amounts of the ethylene carbonate which adversely affect the spinning process and the fiber quality. Advantageously, the spin bath may be maintained at below about 30% by weight ethylene carbonate. Especial advantages are derived, however, with spin baths containing between about 5 and 25% by weight ethylene carbonate.

It has also been found advantageous to employ the present process with elevated spin bath temperatures. Among the advantages derived are improved fiber properties and higher spinning speeds. For example, bath temperatures between about 80 C. and 150 C. may be employed, and with particular advantage, between about 110 and 130 C. In this connection, it

has also been found advantageous to withdraw the formed fiber from such heated spin' bath at speeds between about 30 meters per minute and 200 meters per minute with distances of bath travel ranging from about 5 to 50 inches.

The fibers withdrawn from the coagulating bath are washed to remove coagulating bath materials. Aqueous washing liquids may be used with advantage and these may consist essentially of water. The washing step' may be performed continuously such as by passing the fibers through a water bath or may be performed discontinuously by washing bobbins or cakes of the collected unwashed fibers. Advantageously, the washing step may be performed on thread-advancing devices such as pairs of thread-advancing drums or rollers, or on unitary thread-advancmg devices such as reels. Particular advantages are derived by washing with aqueous liquids which have been heated to above room temperature such as between about 30 C. and the boiling temperature of the washing liquid.

The filamentary materials produced .by the method of this invention may be stretched and heat treated so as to produce oriented products having high tenacity, high elastic recovery, low shrinkage, etc.

This invention will be more fully described by the following examples, although it is understood that the invention is not intended to be limited by these examples. In these examples parts and percen of materials is intended to mean parts and percent by weight.

Example I 20 parts of polyacrylonitrile (average molecular weight 42,000) was dissolved in 80 parts of ethylene carbonate. This solution, after filtering and deaerating under vacuum, was heated to hours with water at 80 C. The washed yarn was later stretched about 10 times inleiigth while heated to a temperature oi. about 150 C., and thereafter relaxed at a temperature of about 140 C. to produce the final product.

During the spinning operation, a quantity of used bath liquid was continually removed from the operating bath and a sufllcient quantity of dipropylene glycol, reclaimed from spent bath liquid as described below, was continually introduced so that the ratio of dipropylenc glycol to ethylene carbonate remained substantially at about 80:20. The final yarn product was very light-colored and of uniform quality having a soft, silky feel. a denier of about 94, a breaking tenacity of about 4.4 grams per denier, and a breaking elongation of about 18%.

The spent bath liquid which was continuously removed from the operating bath was processed and recycled as follows so as to reclaim and reuse both the ethylene carbonate and the dipropylene glycol. The removed bath liquid was cooled to about 0 C. to precipitate ethylene carbonate, and the mixture was thereafter rapidly centriiuged to remove the precipitated ethylene carbonate. The recovered ethylene carbonate was then recycled for use in the preparation of additional polymeric spinning solutions. The mother liquor filtrate was continuously returned to the coagulating bath in controlled quantities, and occasionally, the mother liquor filtrate was distilled at 10 m. m. pressure to remove any impurities or colored matter accumulated in the recycled operating bath.

Example II The procedure and conditions of this example are the same as Example I except for the following: A copolymer was prepared from 95% aerylonitrilc and 5% beta-morpholinoethylvinyl other CHICK: 0 N-CHzCHr-O-CH=CH:

CHzC 2 having an average molecular weight of about 50.000. 18 parts of this wpolymer was dissolved in 82 parts of ethylene carbonate and the resulting spinnlng solution was heated to 110 C. betoreextrusion. Theoperatingcoagulating bath consisted of a technical grade of dlpropylene glycol and 15% ethylene carbonate and was maintained at a temperature of 110 C. The coagulant component in the operating bath, exclusive of ethylene carbonate, consisted 0! approximately 94% dipropylene glycol, 3% tripropylene glycol and 1% propylene glycol and 2% ethylene glycol.

trample III The procedure of this example is the same as Example I with the exception that the coagulating bath is maintained at about 140 C. and the coagulated filaments are drawn through a bath for about inches of bath travel at a speed of about 150 meters per minute.

Among the fiber-forming copolymers which may be employed with advantage in accordance with the process of this invention may be mentioned 'copolymers'of .a'crylonitrile with the following monomeric compounds: vinyl esters (vinyl acetate, vinyl iormate, vinyl benzoate) vinyl ethers, and vinyl ketones; acrylic acid and its esters and amides methacrylic acid and its esters, amides, and nitrile; maleic, itaconic, Iumaric crotonic acids and their esters, amides and nitriles: allyl alcohol and its esters; styrene and nuclear substituted styrenes, e. g. chloroand dichloro styrene; halogenated monoethylenic compounds such as vinyl chloride, vinyl fluoride,

be prepared by any suitable polymerization method such as, for example, the ammonium persulfate catalyzed polymerization of monomer or monomers dissolved or emulsified in water. Molecular weights of these polymers and copolymers are preferably within the range of 10,000 and 250,000, or even higher, although polymers having molecular weights between 30,000 and 150,000 may be used with particular advantage in the production of fibers.

In general, the spinning solutions may be prepared by heating a mixture of the finely divided acrylonitrile polymer or copolymer with the ethylene carbonate solvent until the polymer is 'dissolved. Advantageously, the spinning solution may be maintained, prior to extrusion, at temperatures from about to 150 C., and preferably between about and C. These spinning solutions, preferably. should have a from the coagulating bath of the present process may be washed with aqueous media as previously described and then stretched up to 600-1000 percent or more. The stretching may be accomplished in secondary baths containing materials similar to those suitable for use in the coagulating baths of this invention, or if desired, in other heated media such as, for example, inert liquids, vapors or gases, e. g. steam. Steam may be employed both as the aqueous washing medium and also as the heated stretching medium.

The stretched products may be heat treated while in a relaxed condition at temperatures of between about 100 and 180 C. to improve their physical properties. The expression relaxed condition is intended to include the heat treatment of threads and yarns at no tension at all or preferably, at relatively low tensions such as, for example, between about 0.01 and 0.3 gram per denier.

Oleaginous material such as finishing oils or waxes, may be applied to the yarn and thread products after the heat treating step, or if desired, before the heat treating step.

We claim:

1. The method of forming a shaped article which comprises extruding an acrylonitrile polymer spinning solution containing ethylene carbonate and treating the resulting extruded material with a liquid coagulating medium comprising dipropylene glycol; said polymer containing in the polymer molecule a major portion of acrylonitrile.

2. The method of forming a shaped article which comprises extruding an acrylonitrile polymer spinning solution containing ethylene carbonate as a solvent into a liquid coagulating medium containing, exclusive of ethylene carbonate, at least about 75% by weight dipropylene glycol; said polymer containing in the polymer molecule a major portion of acrylonitrile.

3. The method of forming a shaped article which comprises extruding an acrylonitrile polymer spinning solution containing ethylene carbonate as a solvent into a liquid coagulating medium which, exclusive of ethylene carbonate, consists essentially of dipropylene glycol; said polymer containing in the polymer molecule a major portion of acrylonitrile, and said coagulating medium being maintained at a temperature between about 80 and 150 C.

4. The method of forming a shaped article which comprises extruding an acrylonitrile polymer spinning solution containing ethylene carbonate as a solvent into a liquid coagulating medium containing, exclusive of ethylene carbonate, at least about 75% by weight dipropylene glycol; said polymer containing in the polymer molecule a major portion of acrylonitrile, and

a 8 said coagulating medium containing less than about 80% by weight ethylene carbonate.

5. The method of forming a fiber which comprises extruding through a spinnaret, an acrylonitrile polymer spinning solution containing ethylene carbonate as a solvent into a liquid coagulating medium containing, exclusive of ethylene carbonate, at least about by weight dipropylene glycol; withdrawing the resulting coagulated filamentary material from the coagulating medium and washing it with an aqueous liquid; said polymer containing in the polymer molecule at least about by weight acrylonitrile.

6. A method of forming a fiber according to claim 5 in which the liquid coagulating medium is maintained at a temperature between about 80 and C.

7. A method of forming a fiber according to claim 5 in which the coagulatin medium contains between about 5% and 25% by weight ethylene carbonate.

8. The method of forming a fiber which comprises extruding through a spinnaret, an acrylonitrile polymer spinning solution containing ethylene carbonate as a solvent into a liquid coagulating medium which, exclusive of ethylene carbonate, consists essentially of dipropylene glycol, and contains between about 5% and 25% by weight ethylene carbonate; maintaining said coagulating medium at a temperature between about 80 and 150 C.; withdrawing the resulting coagulated filamentary material from said coagulating medium and .washing it with an aqueous liquid consisting essentially of water; and stretching said washed filamentary material; said polymer containing in the polymer molecule at least about 80% by weight acrylonitrile.

9. The method of forming a fiber which comprises extruding through a spinnaret, an acrylonitrile polymer spinning solution containing ethylene carbonate as a solvent into a liquid coagulating medium which, exclusive of ethylene carbonate, consists essentially of dipropylene lycol, and contains between about 5% and 25% by weight ethylene carbonate; maintaining said coagulating medium at a temperature between about 80 and 150 C.; withdrawing the resulting coagulated filamentary material from said coagulating medium at a speed between about 30 and 200 meters per minute and washing it with a heated aqueous liquid consisting essentially of water; and stretching said washed filamentary material; said polymer containing in the polymer molecule at least about 80% by weight acrylonitrile.

10. A method of forming a fiber according to claim 9 in which the polymer is polyacrylonitrile.

. HERMAN A. BRUSON.

GILMAN S. HOOPER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,420,565 Rugeley et a1. May 13, 1947 2,467,553 Hare Apr. 19, 1949 FOREIGN PATENTS Number Country Date 896,083 France Apr. 17, 1944 

2. THE METHOD OF FORMING A SHAPED ARTICLE WHICH COMPRISES EXTRUDING AN ACRYLONITRILE POLYMER SPINNING SOLUTION CONTAINING ETHYLENE CARBONATE AS A SOLVENT INTO A LIQUID COAGULATING MEDIUM CONTAINING, EXCLUSIVE OF ETHYLENE CARBONATE, AT LEAST ABOUT 75% BY WEIGHT DIPROPYLENE GLYCOL; SAID POLYMER CONTAINING IN THE POLYMER MOLECULE A MAJOR PORTION OF ACRYLONITRILE. 